This invention relates to the art of measurement and it has particular relationship to the determination of the dimensions of a tube; or more generally, a hollow cylinder. Specifically, this invention concerns itself with the determination of the outside diameter, wall thickness and inside diameter of tubes, typically composed of zirconium alloys, which are used as cladding for nuclear fuel elements. The adaptation of this invention to tubes for cladding will be emphasized in the description of this invention which follows in the interest of facilitating the understanding of this invention by relating its description to a concrete adaptation. It is to be understood that the adaptation of the principles of this invention to other uses which may differ materially from its use on nuclear cladding is within the scope of equivalents of this invention, in line with the Doctrine of Equivalents as interpreted and explained in Uniroyal, Inc. v. Rudkin-Wiley Corp. 5 U.S. Patent Quarterly 2d 1434 (CAFC 1988) (at 2, pg. 1443).
This invention is uniquely adapted to the measurement of tubes for use in cladding because it is tailored to deal with the close tolerances, within a few ten-thousands of an inch, which must be maintained in the dimensions of these tubes. Typically, the blank from which the tubes for cladding are made, initially, has an outside diameter of 2.5 inches. It is reduced, typically in four cold pilgering passes, to a diameter nominally of 0.374-inch. The wall thickness is reduced from 0.300-inch to between 0.02290 and 0.02340 typically.
Typically, the processing starts with blanks which are processed in batches. There are about six starting blanks in each batch. Typically, there are four cold pilgering passes for each batch. Each pilgering pass is followed by deburring, pickling and annealing operations. The fourth pilgering pass is followed by straightening; pickling and polishing and other minor operations. Each final tube is then subjected to ultrasonic testing to determine if it meets requirement. During the processing of a batch, (six blanks) samples are cut randomly every two hours for testing. The pilgering reduces the thickness of a blank and multiplies the number of blanks derived from the starting blank and, ultimately, the number of finished tubes. The multiplication of the number of blanks and ultimate tubes are shown in the following Table I:
TABLE I ______________________________________ Typical No. of Reduction in Outside Reduced Blanks No. of Pass Diameter (Inches) & Tubes Produced ______________________________________ 1st 2.5 to 1.75 2 2nd 1.75 to 1.25 6 3rd 1.25 to 0.7 24 4th 0.7 to 0.374 136 ______________________________________
The complete processing of final fourth pass pilgering consumes about five eight-hour shifts. The time taken for each pass and the number of samples cut during each pass (at two-hour intervals) are shown in the following Table II:
TABLE II ______________________________________ Minimum No. of No. of Pass Time in Hours Samples Cut ______________________________________ 1st 2 to 3 1 to 2 2nd 6 3 to 4 3rd 12 to 15 6 to 8 4th 40 20 to 30 ______________________________________
The samples are cut at random from the batch. This invention concerns itself with the determination of the OD, wall thickness and ID of the random samples in the testing, i.e., the inspection of the samples and with the evaluation of the results of the testing.
In accordance with the teaching of the prior art, the inspection of the dimensions of the samples during the processing was carried out manually. The inspection used two instruments: one, to measure the OD and the other, the ID. During the inspection, the minimum and maximum points of the OD and ID were determined. Each sample was placed on a fixture and a laser beam was projected on the sample to produce a shadow. The sample was rotated and displaced longitudinally and the OD measured on the shadow in each position. By comparing the measurements, a maximum and minimum OD was determined for the sample. The sample was then inserted in an air gauge of diameter corresponding to the ID of the sample and rotated and displaced longitudinally, while the pressure of the gauge was read to determine the maximum and minimum ID dimensions for the sample. This data was also recorded. The maximum and minimum dimensions for OD and ID were plotted for a number of samples and based on the plots, a decision was reached as to whether or not, and to what extent, to adjust the pilgering apparatus.
A disadvantage of this practice is that it lends itself to reacting to isolated extreme data. Since only the maximum and minimum extremes are being recorded permanently and used for future evaluation of the operation, the pilgering process is essentially being controlled by extremes. There may be instances where only one point is outside of the controlling limits because of random chance, while actually the pilgering apparatus is operating properly. For example, the sample may have a pit or a burr or a speck of dirt which is picked up as a maximum or minimum. In this case, there is an indication that the setting for the operation should be changed, notwithstanding that the apparatus is operating to produce blanks or tubes within the dimensional limits.
An important disadvantage of the prior-art practice is that it requires two instruments: the fixture and laser for measuring OD and the air pressure gauge for reading ID.
Another disadvantageous aspect of the prior-art practice is that the measurements are, to an extent, dependent on the personal characteristics of the inspector and on his condition at any time. Different inspectors may handle the air gauge which measures the ID differently, or they may read it differently, or they may record the data erroneously, or the number of observations from inspector to inspector may vary. The prior-art process is also time consuming.
It is an object of this invention to overcome the deficiencies and drawbacks of the prior art and to provide a method and apparatus for determining the outside diameter, wall thickness and inside diameter of a sample in whose practice and use the evaluation of the results of the determination shall not be governed by extremes. An important object of this invention is to provide such a method and apparatus in whose practice and use only one instrument shall be required to measure OD, wall thickness and ID. It is also an object of this invention to provide such method and apparatus whose practice and use shall not be materially affected by personal characteristics and condition at any time of the personnel practicing the method or using the apparatus. It is a further object of this invention to provide such method and apparatus whose practice and use shall not be excessively time consuming.